Page:Popular Science Monthly Volume 25.djvu/667

Rh death of the tree which has supported it. The original ancestor of the dodder was a plant with a well-developed root, green stem and leaves, and a twining habit. If its clasping killed the stem which supported it, the effect would be disastrous, for then it would not accomplish the purpose of its climbing. If the twining stem sank into the supporting one, it might cause decay along the line. This decaying would tend to develop rootlets from the side of the climber. The rootlets, used at first merely to assist in climbing, might and must have become modified so as to penetrate the bark to the tissue beneath. A minute absorption of the sap from this would be an assistance. Gradual increase of the amount absorbed would lead to gradual increase in the number of rootlets. And, this continuing, less and less need would be felt for the leaves. As needless organs are sure to degenerate, the leaves would become smaller and smaller, lose more and more of their green color, and finally become the yellow scales and bracts they now are.

Along with the loss of the leaves would go the root. Becoming less necessary, it would get smaller, until finally it would retain only enough of its original character to give the plantlet a start in life, and transmit its qualities to its progeny. Of course, all these changes would be made slowly; but they would come surely. If each succeeding generation of rooting stemmed plants throve better in any way, perfected seed in any greater abundance, or were enabled to crowd out competitors in the struggle for life, we may be sure that the descendants of the favored plants would inherit these good traits, and would send more and more rootlets into the enveloped stem, until at last the habit would become firmly fixed. Thus would be formed a leafless, rootless parasite, so well adapted to hold its own that it would probably exterminate some of the less favored forms.

The commencement of the habit of sending rootlets into stems has been observed in occasional specimens of the convolvulus. Let but this habit grow and be improved upon, as it surely will be if it is found beneficial, and from this small beginning we can look for just such a development as has been found in the dodder. It can not be said that there is always an upward progress in Nature. Degenerate forms exist and thrive as well as regenerate ones. The truth is, that when a plant or an animal can fill a vacant space in the world better by going backward than by going forward, the retreat is sounded. Progress or retrogression, it is the same. The direction best suited to Nature's needs is the one taken; so that, while on the one hand there may be a wonderfully complex organism, perfectly fitted for the struggle for life, on the other hand there may be a very degenerate one equally fitted into its place.